Gillian Anderson was born in Chicago and raised in Puerto Rico, then London, then Grand Rapids, Michigan. In junior high school, she tried very hard to shed her European accent, but by high school she was more interested in standing out than fitting in. Sporting a dyed Mohawk hairdo and a nose ring, wearing combat boots and usually cloaked in black, she was voted her school's "most bizarre girl," and she was arrested on graduation night for breaking and entering school grounds. When she was not acting up, she was acting; she played Juliet in her high school production of Romeo and Juliet, and decided on that balcony set, she would be an actress.

She won rave reviews and a Theater World Award for her 1991 performance off-Broadway in Absent Friends with Brenda Blethyn. Then she came to Hollywood, where she worked intermittently as a waitress between rare and low-paid acting jobs. She had a small role in the wretched The Turning as the romantic interest of a white supremacist, but she was still virtually unknown when she was cast as the skeptical Special Agent Dana Scully on The X-Files.

She met her first husband, Clyde Klotz, when he worked as an X-Files art designer, and they were married by a Buddhist priest on a golf course. When she became pregnant in 1994, the series worked around her swollen midsection by having Agent Scully abducted. After divorcing Klotz, she was briefly linked with actor Adrian Hughes, who had played an alien on X-Files, but Anderson dropped him when she learned he had been convicted of a sex crime. She later dated actor Rod Rowland, best known for his starring role in the mid-1990s sci-fi series Space: Above and Beyond. Her second husband was documentary filmmaker Julian Ozanne, who had been raised in the palace of King Moshoeshoe II of Lesotho, and had previously dated actress Rachel Weisz.

Anderson's occasional movie work has not yet made her a big-screen success. She received good reviews for The House of Mirth with Eric Stoltz, romanced Jon Stewart in Playing by Heart, played the hooker with a heart of gold in Sharon Stone's The Mighty, and went topless in the violent vengeance film Straightheads. She works frequently on stage, and describes herself as 'difficult', due to her determined personality. She loves salmon sushi, her autobiography is titled Mulder, It's Me, and her first name is pronounced with a soft g sound, as 'Jillian'.